1. Field of the Invention
The present invention relates to a process for the metathesis of olefins. More particularly the invention relates to a process wherein the catalyst is part of a distillation structure and the products are simultaneously separated from the reactants and each other by fractional distillation during the reaction.
2. Related Art
Broadly metathesis has been defined as a chemical reaction in which an element or radical in one compound changes places with another element or radical in another compound. See The Van Nostrand Chemist's Dictionary, D. Van Nostrand Company, Inc., 1953, page 463. More specifically olefin metathesis can be defined as the redistribution of alkylidene moieties to give a mixture of olefins. In effect, this reaction takes place via cleavage of the olefin double bond. Generally the reactions of olefinic molecules in the presence of metal-containing catalysts to produce other olefinic molecules are known in the art as “disproportionation”, “dismutation” or “metathesis” reactions.
The metathesis reactions are of considerable interest because of the versatility of the reaction and the numerous olefinic hydrocarbons available from petrochemical sources which are suitable for use in the reaction to yield useful products. One such reaction is the metathesis of propylene with itself to produce n-butene and ethylene. See, for example, U.S. Pat. No. 4,046,832. The reverse reaction is the metathesis of ethylene with n-butene to produce propylene and is disclosed in U.S. Pat. No. 5,026,936. Another use of the metathesis reaction is to produce 2-methyl-2-butene from the reaction of 2-methyl-1-propene and 2-butene. See U.S. Pat. No. 3,702,827.
Finally, the simultaneous disproportionation of olefins and fractional distillation is reported in U.S. Pat. No. 4,709,115. Therein the disproportionation of butene with itself to produce ethylene or propylene and hexene or pentenes is disclosed.
Catalysts that are known to catalyze the metathesis include the oxides of tungsten, rhenium and cobalt/molybdenum.